1. Field of the Invention
The present invention relates to a magnetic reproducing method for reading data signals from a magnetic recording medium such as a magnetic disk by using a thin-film magnetic head.
2. Description of the Related Art
Most of the thin-film magnetic heads currently provided in magnetic recording and reproducing apparatuses such as magnetic disk drive apparatuses and magnetic tape drive apparatuses use a highly sensitive magnetoresistive (MR) effect element. The MR effect element has an output that does not depend on the relative velocity to a magnetic recording medium to read data signals from a magnetic recording medium such as a magnetic disk or a magnetic tape.
A problem with such conventional MR effect elements is that defective products that generate Barkhausen noise in their outputs are produced. The Barkhausen noise is generated primarily because a magnetic domain wall is caught in defects in the magnetic film constituting the MR effect element as the magnetic domain wall moves, and is affected substantially by stress applied to the MR effect element. In practice, when an external or internal stress that exceeds a certain amount is applied, inverse magnetostriction disperses the magnetization in the MR effect element to destabilize the structure of the magnetic domains, making it more likely to cause Barkhausen noise. Such a stress can be caused by a distortion of the structure of the element itself as well as the increase of deformation by the thermal expansion associated with the increase in temperature of the element.
The influence of temperature has become more remarkable than ever before especially in recent current-in-plane (CIP) giant magnetoresistive (GMR) effect elements, current-perpendicular-to-plane (CPP) GMR effect elements, or tunnel magnetoresistive (TMR) effect elements, which sense signal magnetic fields with extremely high sensitivities.
Furthermore, in order to stably control the flying height of a thin-film magnetic head, which is set to an ultra-small value in a recent magnetic disk drive apparatus, a technique has come into adoption in which a heating element is provided within a thin-film magnetic head and the end of the head element is caused to be protruded in the direction of the magnetic disk by the heat generated by the heating element to adjust the flying height (see, for example, U.S. Pat. No. 5,991,113). With this technique, thermal asperities and crashes are avoided to maintain good read and write characteristics. However, the heat generated by such a heating element further heats the MR effect element and portions around the MR effect element, and can further increase the influence of the temperature variation.
Approaches to preventing the Barkhausen noise in MR effect elements, which is likely to receive a significant influence of the temperature variation, have been proposed. For example, Japanese Patent Publication No. 2002-133621A proposes a method for determining whether an MR effect element is acceptable or defective by measuring noise generated in response to various values of sense currents flowing through an MR effect element. Here, in this method with a larger sense current, the determination is performed under the condition of a high temperature because the temperature of the MR effect element inevitably becomes high. Further, Japanese Patent Publication No. 06-84116A discloses a technique that gradually increases a sense current passed through an MR effect head to prevent the formation of a magnetic domain structure that is likely to generate noise due to a stress or the like caused by a rapid change in temperature.
However, it has been significantly difficult to solve the problem of noise generated under a low temperature with the related art described above.
Recently, magnetic recording and reproducing apparatuses, especially magnetic disk drive apparatuses, are mounted extensively as storage memories for storing large volumes of data such as audio/video data, to mobile devices that are often used out of doors such as notebook-size computers or cellular phones. As a result, the apparatuses are used in a rather wide temperature range of the use environment. Especially, in some cases, normal performance of the apparatus is required to be guaranteed even at an extremely low temperature, for example, such as −30° C. (degree Celsius).
However, some thin-film magnetic heads actually manufactured have a noise such as Barkhausen noise that exceeds the allowable number in the output under such a low temperature. Here, in order to screen such heads with significant noise, there has been no other way than that the output characteristic at the low temperature of the head is measured under the condition that the head flies on a magnetic disk after completing the head gimbal assembly (HGA) production by attaching the head to a suspension. That is, it has been significantly difficult that a head to generate a noise in such a low temperature is predicted. As a result, in the case that a head is determined as a defective one, the value-added whole HGA including the head must be discarded. Therefore, the loss per defective head becomes large, which is likely to bring an increase in cost of production.
Further, even if the sense currents are used for screening defective heads as described in Japanese Patent Publication No. 2002-133621A, only the output characteristic of the head under a high temperature can be evaluated. The same applies to the technique described in Japanese Patent Publication No. 06-84116A, and therefore, the noise generation in a low temperature has ever been problematic.